Crosslinkable polymeric compositions with methyl-radical scavengers and articles made therefrom

ABSTRACT

Crosslinkable polymeric compositions for use in, for instance, cable insulation layers, are disclosed. The crosslinkable polymeric compositions comprise an ethylene-based polymer, an organic peroxide, a crosslinking coagent, and a methyl-radical scavenger comprising at least one derivative of 2, 2, 6, 6-tetramethyl-1-piperidinyloxy (“TEMPO”), such as 4-acryloxy-2, 2, 6, 6-tetramethylpiperidine-N-oxyl, 4-allyloxy-2, 2, 6, 6-tetramethylpiperidine-N-oxyl, and bis (2, 2, 6, 6-tetramethyl-1-piperidinyloxy-4-yl) sebacate, and combinations of two or more thereof, wherein ratio of crosslinking coagent to organic peroxide is less than 1.72:1 on a molar basis. A crosslinked article prepared from a crosslinkable polymeric composition is also disclosed, the crosslinkable polymeric composition comprising, inter alia, a methyl-radical scavenger comprising at least one TEMPO derivative. In addition, a coated conductor comprising a conductive core and a polymeric layer at least partially surrounding the conductive core is disclosed, wherein at least a portion of the polymeric layer comprises the crosslinked article.

TECHNICAL FIELD

The present disclosure relates to crosslinkable polymeric compositionscomprising an ethylene-based polymer, an organic peroxide, acrosslinking coagent, and a methyl-radical scavenger comprising at leastone derivative of 2,2,6,6-tetramethyl-1-piperidinyloxy (“TEMPO”), andarticles made therefrom.

BACKGROUND

Medium voltage (“MV”), high voltage (“HV”), and extra-high voltage(“EHV”) cables typically contain a crosslinked polymeric material as aninsulation layer, such as a crosslinked polyethylene. Such crosslinkedpolymeric materials can be prepared from a crosslinkable polymericcomposition having a peroxide initiator. Crosslinking provides valuableimprovements in the thermomechanical properties of the crosslinkedpolymeric material.

The peroxide initiators used for crosslinking do, however, createbyproducts that require removal from the crosslinked polymeric material.For instance, when dicumyl peroxide is used as the peroxide initiator,the crosslinking reactions yield volatile byproducts such asacetophenone, cumyl alcohol, and methane. If not removed, thesebyproducts can negatively impact the quality of the cable comprising thecrosslinked polymeric material. Byproduct removal must occur after thecrosslinked polymeric material is formed into an insulation layer (e.g.,by degassing) but before a jacketing layer is placed over the insulationlayer.

Further, premature crosslinking, commonly known as “scorch,” can beencountered during extrusion of the crosslinked polymeric material.Better scorch protection increases the processability of the crosslinkedpolymeric material.

Although advances have been achieved in the field of crosslinkablepolymeric compositions, improvements are still desired.

SUMMARY OF THE DISCLOSURE

Crosslinkable polymeric compositions for use in, for example, cableinsulation layers, are disclosed. The crosslinkable polymericcompositions comprise, inter alia, an ethylene-based polymer, an organicperoxide, a crosslinking coagent, and a methyl-radical scavengercomprising at least one TEMPO derivative, wherein the ratio ofcrosslinking coagent to organic peroxide is less than 1.72:1 on a molarbasis. Inclusion of the at least one TEMPO derivative in thecrosslinkable polymeric compositions provides a composition havingimproved properties, such as reduced byproduct offgassing, increasedcrosslink density, and improved scorch protection.

Crosslinked polymeric articles prepared from crosslinkable polymericcompositions are also disclosed, the crosslinkable polymericcompositions comprising, inter alia, a methyl-radical scavengercomprising at least one TEMPO derivative and a crosslinking coagent toorganic peroxide ratio less than 1.72:1 on a molar basis. In addition,coated conductors comprising a conductive core and a polymeric layer atleast partially surrounding the conductive core are disclosed, whereinat least a portion of the polymeric layer comprises the crosslinkedpolymeric articles.

BRIEF DESCRIPTION OF THE DRAWING

Reference is made to the accompanying drawing in which:

FIG. 1 is a plot of peak area versus methane used as a calibration curvefor methane quantification.

DETAILED DESCRIPTION OF THE DISCLOSURE Crosslinkable PolymericComposition

One component of the crosslinkable polymeric compositions describedherein is an ethylene-based polymer. As used herein, “ethylene-based”polymers are polymers prepared from ethylene monomers as the primary(i.e., greater than 50 weight percent (“wt %”)) monomer component,though other comonomers may also be employed. “Polymer” means amacromolecular compound prepared by reacting (i.e., polymerizing)monomers of the same or different type, and includes homopolymers andinterpolymers. “Homopolymer” means a polymer consisting of repeatingunits derived from a single monomer type, but does not exclude residualamounts of other components used in preparing the homopolymer, such aschain transfer agents. “Interpolymer” means a polymer prepared by thepolymerization of at least two different monomer types. The generic term“interpolymer” includes copolymers, usually employed to refer topolymers prepared from two different monomer types, and polymersprepared from more than two different monomer types (e.g., terpolymers,quaterpolymers, and so on).

In some embodiments, the ethylene-based polymer can be an ethylenehomopolymer. In some embodiments, the ethylene-based polymer can be anethylene/alpha-olefin (“α-olefin”) interpolymer having an α-olefincontent of at least 1 wt %, at least 5 wt %, at least 10 wt %, at least15 wt %, at least 20 wt %, or at least 25 wt % based on the entireinterpolymer weight. These interpolymers can have an α-olefin content ofless than 50 wt %, less than 45 wt %, less than 40 wt %, or less than 35wt % based on the entire interpolymer weight. When an α-olefin isemployed, the α-olefin can be a C₃₋₂₀ (i.e., having 3 to 20 carbonatoms) linear, branched, or cyclic α-olefin. Examples of C₃₋₂₀ α-olefinsinclude propene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene,1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, and 1-octadecene. Theα-olefins can also have a cyclic structure such as cyclohexane orcyclopentane, resulting in an α-olefin such as 3-cyclohexyl-1-propene(allyl cyclohexane) and vinyl cyclohexane. Illustrativeethylene/α-olefin interpolymers include ethylene/propylene,ethylene/1-butene, ethylene/1-hexene, ethylene/1-octene,ethylene/propylene/1-octene, ethylene/propylene/1-butene, andethylene/1-butene/1-octene.

In some embodiments, the ethylene-based polymer can be used alone or incombination with one or more other types of ethylene-based polymers(e.g., a blend of two or more ethylene-based polymers that differ fromone another by monomer composition and content, catalytic method ofpreparation, etc.). If a blend of ethylene-based polymers is employed,the polymers can be blended by any in-reactor or post-reactor process.

In some embodiments, the ethylene-based polymer can be selected from thegroup consisting of low-density polyethylene (“LDPE”),linear-low-density polyethylene (“LLDPE”), very-low-density polyethylene(“VLDPE”), and combinations of two or more thereof.

In some embodiments, the ethylene-based polymer can be a LDPE. LDPEs aregenerally highly branched ethylene homopolymers, and can be prepared viahigh pressure processes (i.e., HP-LDPE). LDPEs suitable for use hereincan have a density ranging from 0.91 to 0.94 g/cm³. In some embodiments,the ethylene-based polymer is a high-pressure LDPE having a density ofat least 0.915 g/cm³, but less than 0.94 g/cm³, or less than 0.93 g/cm³.Polymer densities provided herein are determined according to ASTMInternational (“ASTM”) method D792. LDPEs suitable for use herein canhave a melt index (I₂) of less than 20 g/10 min., or ranging from 0.1 to10 g/10 min., from 0.5 to 5 g/10 min., from 1 to 3 g/10 min., or an I₂of 2 g/10 min. Melt indices provided herein are determined according toASTM method D1238. Unless otherwise noted, melt indices are determinedat 190° C. and 2.16 Kg (i.e., I₂). Generally, LDPEs have a broadmolecular weight distribution (“MWD”) resulting in a relatively highpolydispersity index (“PDI;” ratio of weight-average molecular weight tonumber-average molecular weight).

In some embodiments, the ethylene-based polymer can be a LLDPE. LLDPEsare generally ethylene-based polymers having a heterogeneousdistribution of comonomer (e.g., α-olefin monomer), and arecharacterized by short-chain branching. For example, LLDPEs can becopolymers of ethylene and α-olefin monomers, such as those describedabove. LLDPEs suitable for use herein can have a density ranging from0.916 to 0.925 g/cm³. LLDPEs suitable for use herein can have a meltindex (I₂) ranging from 1 to 20 g/10 min., or from 3 to 8 g/10 min.

In some embodiments, the ethylene-based polymer can be a VLDPE. VLDPEsmay also be known in the art as ultra-low-density polyethylenes(“ULDPE”). VLDPEs are generally ethylene-based polymers having aheterogeneous distribution of comonomer (e.g., α-olefin monomer), andare characterized by short-chain branching. For example, VLDPEs can becopolymers of ethylene and α-olefin monomers, such as one or more ofthose α-olefin monomers described above. VLDPEs suitable for use hereincan have a density ranging from 0.87 to 0.915 g/cm³. VLDPEs suitable foruse herein can have a melt index (I₂) ranging from 0.1 to 20 g/10 min.,or from 0.3 to 5 g/10 min.

In addition to the foregoing, the ethylene-based polymer can contain oneor more polar comonomers, such as acrylates or vinyl acetates.Additionally, blends of non-polar ethylene-based polymers, such as thosedescribed above, and polar copolymers (e.g., those copolymers containingone or more types of polar comonomers), may also be employed.Furthermore, polyolefin elastomers, such as those commercially availableunder the trade name ENGAGE™ from The Dow Chemical Company, may be usedas the ethylene-based polymer or in combination with one or more of theabove-described ethylene-based polymers. Polyolefin elastomers suitablefor use herein can have a density ranging from 0.857 g/cm³ to 0.908g/cm³. Polyolefin elastomers suitable for use herein can have a meltindex (I₂) ranging from 0.1 to 30 g/10 min., or from 0.5 to 5 g/10 min.

In some embodiments, the ethylene-based polymer can comprise acombination of any two or more of the above-described ethylene-basedpolymers.

Production processes used for preparing ethylene-based polymers arewide, varied, and known in the art. Any conventional or hereafterdiscovered production process for producing ethylene-based polymershaving the properties described above may be employed for preparing theethylene-based polymers described herein. In general, polymerization canbe accomplished at conditions known in the art for Ziegler-Natta,chromium oxide, or Kaminsky-Sinn type polymerization reactions, that is,at temperatures from 0 to 250° C., or 30 or 200° C., and pressures fromatmospheric to 10,000 atmospheres (approximately 1,013 MegaPascals(“MPa”)). In most polymerization reactions, the molar ratio of catalystto polymerizable compounds employed is from 10⁻¹²:1 to 10-1:1, or from10⁻⁹:1 to 10⁻⁵:1.

An example of an ethylene-based polymer suitable for use herein islow-density polyethylene having a density of 0.92 g/cm³ and a melt index(I₂) of 2 g/10 min.

The crosslinkable polymeric composition further comprises an organicperoxide. As used herein, “organic peroxide” denotes a peroxide havingthe structure: R¹—O—O—R² or R¹—O—O—R—O—O—R², where each of R¹ and R² isa hydrocarbyl moiety, and R is a hydrocarbylene moiety.

As used herein, “hydrocarbyl” denotes a univalent group formed byremoving a hydrogen atom from a hydrocarbon (e.g., ethyl, phenyl)optionally having one or more heteroatoms. As used herein,“hydrocarbylene” denotes a bivalent group formed by removing twohydrogen atoms from a hydrocarbon optionally having one or moreheteroatoms. The organic peroxide can be any dialkyl, diaryl, dialkaryl,or diaralkyl peroxide, having the same or differing alkyl, aryl,alkaryl, or aralkyl moieties. In some embodiments, each of R¹ and R² isindependently a C₁ to C₂₀ or C₁ to C₁₂ alkyl, aryl, alkaryl, or aralkylmoiety. In some embodiments, R can be a C₁ to C₂₀ or C₁ to C₁₂ alkylene,arylene, alkarylene, or aralkylene moiety. In some embodiments, R, R¹,and R² can have the same or a different number of carbon atoms andstructure, or any two of R, R¹, and R² can have the same number ofcarbon atoms while the third has a different number of carbon atoms andstructure.

Organic peroxides suitable for use herein include mono-functionalperoxides and di-functional peroxides. As used herein, “mono-functionalperoxides” denote peroxides having a single pair of covalently bondedoxygen atoms (e.g., having a structure R—O—O—R). As used herein,“di-functional peroxides” denote peroxides having two pairs ofcovalently bonded oxygen atoms (e.g., having a structure R—O—O—R—O—O—R).In some embodiments, the organic peroxide is a mono-functional peroxide.

Exemplary organic peroxides include dicumyl peroxide (“DCP”), tert-butylperoxybenzoate, di-tert-amyl peroxide (“DTAP”),bis(alpha-t-butyl-peroxyisopropyl) benzene (“BIPB”), isopropylcumylt-butyl peroxide, t-butylcumylperoxide, di-t-butyl peroxide,2,5-bis(t-butylperoxy)-2,5-dimethylhexane,2,5-bis(t-butylperoxy)-2,5-dimethylhexyne-3,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, isopropylcumylcumylperoxide, butyl 4,4-di(tert-butylperoxy) valerate,di(isopropylcumyl) peroxide, and combinations of two or more thereof. Insome embodiments, only a single type of organic peroxide is employed. Insome embodiments, the organic peroxide is dicumyl peroxide.

The crosslinkable polymeric composition further comprises a crosslinkingcoagent. Examples of crosslinking coagents include polyallylcrosslinking coagents such as triallyl isocyanurate (“TAIC”), triallylcyanurate (“TAC”), triallyl trimellitate (“TATM”),N2,N2,N4,N4,N6,N6-hexaallyl-1,3,5-triazine-2,4,6-triamine (“HATATA”),triallyl orthoformate, pentaerythritol triallyl ether, triallyl citrate,and triallyl aconitate, α-methyl styrene dimer (“AMSD”), acrylate-basedcoagents such as trimethylolpropane triacrylate (“TMPTA”),trimethylolpropane trimethylacrylate (“TMPTMA”), ethoxylated bisphenol Adimethacrylate, 1,6-hexanediol diacrylate, pentaerythritoltetraacrylate, dipentaerythritol pentaacrylate, tris(2-hydroxyethyl)isocyanurate triacrylate, and propoxylated glyceryl triacrylate,vinyl-based coagents such as polybutadiene having a high 1,2-vinylcontent, trivinyl cyclohexane (“TVCH”), and other coagents such as thosedescribed in U.S. Pat. Nos. 5,346,961 and 4,018,852. The crosslinkingcoagent may comprise a single coagent or a blend of coagents (i.e., acombination of two or more coagents).

The crosslinkable polymeric composition further comprises amethyl-radical scavenger comprising at least one derivative of2,2,6,6-tetramethyl-1-piperidinyloxy (“TEMPO”) having a structure offormula (I)

As used herein, derivatives of TEMPO include, for example,4-acryloxy-2,2,6,6-tetramethylpiperidine-N-oxyl (“acrylate TEMPO”)having a structure of formula (II) (CAS: 21270-85-9)

4-allyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl (“allyl TEMPO”) having astructure of formula (III), (CAS: 217496-13-4)

bis(2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl) sebacate (“bis TEMPO”)having a structure of formula (IV), (CAS: 2516-92-9)

and combinations of two or more thereof. The methyl-radical scavengercan comprise a TEMPO derivative selected from any one of acrylate TEMPO,allyl TEMPO, or bis TEMPO, and combinations of two or more thereof.

In some embodiments, the crosslinkable polymeric composition cancomprise the ethylene-based polymer in an amount ranging from 1 to 99.9wt %, from 90 to 99.9 wt %, or from 97.72 to 98.6 wt %, based on theentire crosslinkable polymeric composition weight. In addition, thecrosslinkable polymeric composition can comprise the organic peroxide inan amount ranging from 0.1 to 3 wt %, from 0.1 to 2 wt %, or from 0.1 to0.95 wt %, based on the entire crosslinkable polymeric compositionweight. Further, the crosslinkable polymeric composition can comprisethe crosslinking coagent in an amount ranging from 0.1 to 5.2 wt %, from0.2 to 1 wt %, or from 0.4 to 0.5 wt %, based on the entirecrosslinkable polymeric composition weight. Still further, thecrosslinkable polymeric composition can comprise the methyl-radicalscavenger in an amount ranging from 0.05 to 10 wt %, from 0.16 to 5 wt%, from 0.5 to 1 wt %, or from 0.68 to 0.72 wt %, based on the entirecrosslinkable polymeric composition weight. In some embodiments, theratio of crosslinking coagent and organic peroxide is equal to or lessthan 1.72:1 on a molar basis (i.e., moles crosslinking coagent/molesorganic peroxide), equal to or less than 1.08:1 on a molar basis, orequal to or less than 0.51:1 on a molar basis.

In addition to the components described above, the crosslinkablepolymeric composition may also contain one or more additives including,but not limited to, scorch retardants, antioxidants, processing aids,fillers, coupling agents, ultraviolet absorbers or stabilizers,antistatic agents, nucleating agents, slip agents, plasticizers,lubricants, viscosity control agents, tackifiers, anti-blocking agents,surfactants, extender oils, acid scavengers, flame retardants, watertree retardants, electrical tree retardants, voltage stabilizers, andmetal deactivators. Additives, other than fillers, are typically used inamounts ranging from 0.01 or less to 10 or more wt % based on totalcomposition weight. Fillers are generally added in larger amounts,although the amount can range from as low as 0.01 or less to 65 or morewt % based on the total composition weight. Illustrative examples offillers include clays, precipitated silica and silicates, fumed silica,calcium carbonate, ground minerals, aluminum trihydroxide, magnesiumhydroxide, and carbon blacks with typical arithmetic mean particle sizeslarger than 15 nanometers.

Further, exemplary antioxidants include hindered phenols (e.g., tetrakis[methylene (3,5-di-t-butyl-4-hydroxyhydrocinnamate)] methane),less-hindered phenols, and semi-hindered phenols, phosphates,phosphites, and phosphonites (e.g., tris (2,4-di-t-butylphenyl)phosphate), thio compounds (e.g., distearyl thiodipropionate, dilaurylthiodipropionate), various siloxanes, and various amines (e.g.,polymerized 2,2,4-trimethyl-1,2-dihydroquinoline). In some embodiments,the antioxidant is selected from the group consisting of distearylthiodipropionate, dilauryl thiodipropionate,octadecyl-3,5-di-t-butyl-4-hydroxyhydrocinnamate, benzenepropanoic acid,3,5-bis(1,1-dimethylethyl)-4-hydroxy-thiodi-2,1-ethanediyl ester,stearyl 3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate,octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate,2,4-bis(dodecylthiomethyl)-6-methylphenol,4,4′-thiobis(6-tert-butyl-m-cresol), 4,6-bis(octylthiomethyl)-o-cresol,1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione, pentaerythritoltetrakis(3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate),2′,3-bis[[3-[3,5-di-tert-butyl-4-hydroxyphenyl]propionyl]]propionohydrazide, and combinations of two or more thereof.Commercially available examples of antioxidants suitable for use in thedisclosed crosslinkable polymeric materials include CYANOX™ 1790available from the Cytec Solvay Group and IRGANOX™ PS 802 available fromBASF SE. Suitable antioxidants may also comprise hindered amine lightstabilizers (“HALS”).

Antioxidants, when present, can be used in amounts ranging from 0.01 to5 wt %, from 0.01 to 1 wt %, from 0.1 to 5 wt %, from 0.1 to 1 wt %, orfrom 0.1 to 0.5 wt %, based on the total weight of the crosslinkablepolymeric composition.

Preparation of Crosslinkable Polymeric Composition

Preparation of the cross-linkable polymeric composition can comprisecompounding the above-described components. For example, compounding canbe performed by either (1) compounding all components into theethylene-based polymer, or (2) compounding all the components except forone or more of the organic peroxide, one or more of crosslinkingcoagent, and one or more of methyl-radical scavenger, which can besoaked in as described below. Compounding of the crosslinkable polymericcomposition can be effected by standard equipment known to those skilledin the art. Examples of compounding equipment are internal batch mixers,such as a Brabender™, Banbury™, or Bolling™ mixer. Alternatively,continuous single or twin screw, mixers can be used, such as a Farrel™continuous mixer, a Werner and Pfleiderer™ twin screw mixer, or a Buss™kneading continuous extruder. Compounding can be performed at atemperature of greater than the melting temperature of theethylene-based polymer up to a temperature above which theethylene-based polymer begins to degrade. In some embodiments,compounding can be performed at a temperature ranging from 100 to 200°C., or from 110 to 150° C.

In some embodiments, the ethylene-based polymer and any optionalcomponents can first be melt compounded according to the above-describedprocedure and pelletized. Next, the organic peroxide, the crosslinkingcoagent, and the methyl-radical scavenger comprising at least one TEMPOderivative can be soaked into the resulting ethylene-based polymercompound, either simultaneously or sequentially. In some embodiments,one or more of the organic peroxide, the coagent, and the TEMPOderivative can be premixed at the temperature above the meltingtemperature of the organic peroxide, the coagent, and the TEMPOderivative, whichever is greatest or above the melt temperature of thecorresponding mixture, followed by soaking the ethylene-based polymercompound in the resulting mixture of the organic peroxide, thecrosslinking coagent, and the TEMPO derivative at a temperature rangingfrom 30 to 100° C., from 50 to 90° C., or from 60 to 80° C., for aperiod of time ranging from 1 to 168 hours, from 1 to 24 hours, or from3 to 12 hours.

The resulting crosslinkable polymeric composition can have certainenhanced properties. Though not wishing to be bound by theory, it isbelieved that utilizing a disclosed crosslinking coagent together with amethyl-radical scavenger comprising at least one TEMPO derivative cansurprisingly provide superior curing and scorch resistance properties aswell as decreased undesired byproduct generation.

Crosslinked Polymeric Composition

The above-described crosslinkable polymeric compositions can be cured orallowed to cure in order to form a crosslinked polymeric composition.Such curing can be performed by subjecting the crosslinkable polymericcomposition to elevated temperatures in a heated cure zone, which can bemaintained at a temperature in the range of 175 to 260° C. The heatedcure zone can be heated by pressurized steam or inductively heated bypressurized nitrogen gas. Thereafter, the crosslinked polymericcomposition can be cooled (e.g., to ambient temperature).

The crosslinking process can create volatile decomposition byproducts inthe crosslinked polymeric composition. Following crosslinking, thecrosslinked polymeric composition can undergo degassing to remove atleast a portion of the volatile decomposition byproducts. Degassing canbe performed at a degassing temperature, a degassing pressure, and for adegassing time period to produce a degassed polymeric composition. Insome embodiments, the degassing temperature can range from 50 to 150°C., or from 60 to 80° C. In some embodiments, the degassing temperatureis 65 to 75° C. Degassing can be conducted under standard atmospherepressure.

Cable Core

The initial cable core containing inner and outer semiconductive andinsulation layers can be prepared with various types of extruders, e.g.,single or twin screw types. A description of a conventional extruder canbe found in U.S. Pat. No. 4,857,600. An example of co-extrusion and anextruder therefore can be found in U.S. Pat. No. 5,575,965. A typicalextruder has a hopper at its upstream end and a die at its downstreamend. The hopper feeds into a barrel, which contains a screw. At thedownstream end, between the end of the screw and the die, there is ascreen pack and a breaker plate. The screw portion of the extruder isconsidered to be divided up into three sections, the feed section, thecompression section, and the metering section, and two zones, the backheat zone and the front heat zone, the sections and zones running fromupstream to downstream. In the alternative, there can be multipleheating zones (more than two) along the axis running from upstream todownstream. If it has more than one barrel, the barrels are connected inseries. The length to diameter ratio of each barrel is in the range ofabout 15:1 to about 30:1.

Following extrusion, the resulting initial cable core can undergo acrosslinking process to crosslink the insulation and both inner andouter semiconductive layers. For example, the initial cable core can bepassed into a heated cure zone downstream of the extrusion die. Theheated cure zone can be maintained at a temperature in the range ofabout 150 to about 350° C., or in the range of about 170 to about 250°C. The heated cure zone can be heated by pressurized steam, orinductively heated pressurized nitrogen gas. Following the crosslinkingprocess, the cable core having a crosslinked insulation, inner, andouter semiconductive layers can be cooled (e.g., to room temperature).

Degassing

The crosslinking process can create volatile decomposition byproducts inthe crosslinked insulation layer. The term “volatile decompositionproducts” denotes decomposition products formed during the curing step,and possibly during the cooling step, by decomposition and reaction ofthe free radical generating agent (e.g., dicumyl peroxide). Suchbyproducts can comprise alkanes, such as methane. Additional byproductscan include alcohols. Such alcohols can comprise the alkyl, aryl,alkaryl, or aralkyl moieties of the above-described organic peroxide.

For instance, if dicumyl peroxide is employed as a crosslinking agent,the byproduct alcohol is cumyl alcohol. Other decomposition products caninclude ketone byproducts from the above-described organic peroxide. Forexample, acetophenone is a decomposition byproduct of dicumyl peroxide.

Following crosslinking, the crosslinked insulation layer can undergodegassing to remove at least a portion of volatile decompositionbyproducts. Degassing can be performed at a degassing temperature, adegassing pressure, and for a degassing time period to produce adegassed cable core. In various embodiments, the degassing temperaturecan range from 50 to 150° C., or from 60 to 80° C. In an embodiment, thedegassing temperature is 65 to 75° C. Degassing can be conducted understandard atmospheric pressure (i.e., 101,325 Pa).

Alternating current cables can be prepared according to the presentdisclosure, which can be LV, MV, HV, or EHV cables. Further, directcurrent cables can be prepared according to the present disclosure,which can include high or extra-high voltage cables.

EXAMPLES AND TESTING Raw Materials

A low-density polyethylene (“LDPE”) is employed that has a melt index(I₂) of approximately 2 g/10 min. and a density of 0.92 g/cm³. LDPE 1 isproduced by The Dow Chemical Company and contains 0.13% distearylthiodipropionate (“DSTDP”), 0.09% CYANOX™ 1790 and about 20 ppm UVINUL4050. LDPE 2 is produced by The Dow Chemical Company and contains 0.09%DSTDP, 0.06% CYANOX™ 1790 and about 14 ppm UVINUL 4050.

CYANOX™ 1790 is a commercially available antioxidant having the chemicalname1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6-trione,available from Cytec Industries. It is used as received.

Disteayl thiodipropionate (“DSTDP”) is a commercially availableantioxidant available from Cytec. It is used as received. UVINUL™ 4050is a commercially available UV stabilizer having the chemical name1,6-hexamethylenebis[N-formyl-N-(2,2,6,6-tetramethylpiperidin-4-yl)amine],available from BASF. It is used as received.

Dicumyl peroxide (“DCP”) is commercially available from ShanghaiFangruida Chemicals Co., Ltd.

Triallyl isocyanurate (“TAIC”) is commercially available from ShanghaiFangruida Chemicals Co., Ltd. It is used as received.

Triallyl cyanurate (“TAC”) and triallyl trimellitate (“TATM”) arecommercially available from Sinopharm Chemical. Both are used asreceived.

TMPTA and TMPTMA are commercially available from Sartomer. Both are usedas received.

HATATA is prepared by adding 3.69 g (0.02 mol) cyanuric acid and 8.90 g(0.064 mol) sodium carbonate into 30 g of 1,4-dioxane in a three-neckflask. While stirring, heat the mixture to 75° C., and stir for anadditional 5 minutes upon reaching 75° C. Next, gradually add 10.22 g(0.1 mol) diallylamine dropwise over about 15 minutes, then add 2.8 g ofsodium hydroxide (0.07 mol) and raise the temperature to about 90° C.Keep the reaction mixture at 90° C. for 5 hours. Thereafter, cool thereaction mixture to room temperature and filter using vacuum filtrationwith a sand-core funnel to remove insoluble salts. The resultingfiltrate is distilled under reduced pressure to recover the solvent, andthe residue is dissolved in petroleum ether and further purified throughsilica gel column. This is performed by first transferring the liquidfiltrate from the flask to the silica gel column and use 2 mL ofpetroleum ether to wash the flask and transfer the solution to thesilica gel. The silica gel is 300 mesh and is used as the stationaryphase; the petroleum ether is used as the eluent.

TEMPO is commercially available from TCI. It is used as received.

Bis TEMPO is commercially available from Ningbo Sialon Chem. Co. Ltd. Itis used as received.

Acrylate TEMPO can be prepared by known techniques, such as thosedisclosed in Hyslop D. K., Parent J. S., Macromolecules, 2012; 45,8147-8154. For instance, acryloyl chloride (632 mg, 0.57 mL, 6.98 mmol)in toluene (2.03 mL) was added dropwise to a solution of 4-hydroxylTEMPO (4-hydroxyl-2,2,6,6-tetramethyl-1-piperidinyloxy) (1 g, 5.81 mmol)and triethylamine (706 mg, 0.97 mL, 6.98 mmol) in toluene (14.4 mL), andthe mixture was stirred at room temperature for 16 h. The resultingsolution was filtered before removing solvent under vacuum, yieldingorange crystals that were recrystallized from cyclohexane.

Allyl TEMPO can be prepared by adding 1.2 equivalents of sodium hydrideto a solution of 1 equivalent of TEMPO in tetrahydrofuran. Allylbrodmide is added dropwise to the solution and the mixture is stirred atreflux for 12 hours. The mixture is then quenched by addition ofsaturated ammonium chloride and extracted with ethyl acetate. Thecombined organic layers are then washed with brine, dried over sodiumsulfate, and concentrated under reduced pressure. The crude material ispurified by flash column chromatography to obtain the allyl TEMPO.

Moving Die Rheometer

Perform moving die rheometer (“MDR”) testing at 180° C. and 140° C.according to the methods described in ASTM D5289 on an AlphaTechnologies MDR 2000 using samples cut from the sheet prepared by thetwo-roll mill or soaked pellets.

Scorch Improvement

Scorch Improvement of a sample X prepared with both crosslinking coagentand a methyl-radical scavenger is calculated using equation (I) below:

SI=ts1@140° C.−ts1′@140° C.  (I)

where SI is the scorch improvement, ts1@140° C. is the scorch time ofsample X measured by MDR at 140° C., and ts1′@140° C. is the predictedscorch for sample X but having no methyl-radical scavenger and nocrosslinking coagents, where the prediction is based on the crosslinkdensity (MH−ML) of sample X. The predicted scorch time is calculatedaccording to equation (2) below:

ts1′@140° C.=−4.10+142.84/(MH−ML)@180° C.  (II)

where:

(MH−ML)@180° C. is the crosslink density of sample X measured by MDR at180° C. Equation (I) is determined based on comparison of five samplesprepared without a methyl-radical scavenger and crosslinking coagents todetermine the relationship between scorch time and crosslink density forsamples having no crosslinking coagent and no methyl-radical scavenger.

TABLE 1 Curing/scorch results at different DCP loading ts1@140° C., MH −ML@180° C., LDPE 1, % DCP, % min. dN*m 99.4 0.6 130.00 1.05 99.1 0.980.46 1.81 98.8 1.2 50.66 2.52 98.5 1.5 38.80 3.26 98.2 1.8 31.77 3.89

Equation (2) is the relationship between crosslink density (MH−ML)@180°C. and scorch time (ts1′@140° C.) of the sample containing nomethyl-radical scavenger and no crosslinking coagents. Therefore, thescorch time (ts1′@140° C.) of the sample with no methyl-radicalscavenger and no crosslinking coagents (ts1′@140° C.) at a givencrosslink density (MH−ML)@180° C. can be predicted by this equation. TheSI value suggests how the addition of both a crosslinking coagents and amethyl-radical scavenger will impact the scorch time compared to thesample without both the crosslinking coagent and methyl-radicalscavenger. A negative value means reduced the anti-scorch property,while a positive value means improved anti-scorch property, with thegreater the positive value the better.

Methane Content (Multiple Headspace Extraction Via Headspace GasChromatography) Methane Content is Measured on Plaque Samples

Compression Molding to Prepare Plaques

-   -   1. Put about 30 g of sample into a 1-mm thickness mold between        two PET films. Then put this loaded mold into a hot press        machine (LabTech).    -   2. Preheating at 120° C. for 10 minutes.    -   3. Venting for 8 times and 0.2 s for each.    -   4. Close the platens to apply 15 MPa pressure to mold for 20        minutes. Meanwhile increase the temperature to 182° C. within        6.5 minutes.    -   5. Keep a continued 15 MPa on the mold and cooling to 24° C.    -   6. Take out the mold from machine.

Headspace Gas Chromatography (GC) Sampling

-   -   1. Remove the cured plaque with two PET films adhered on both        sides from mold    -   2. Peel off the PET film quickly.    -   3. Cut out two sheets of the plaque's center area (0.3 g), and        put them into two headspace GC vials, then seal the vials        immediately. ˜30 seconds from step 2 to 3    -   4. Weigh the sealed GC headspace vial, and the sample weight        could be calculated by the difference between the empty vial and        the vial with sample.

GC Conditions for Plaque Analyses

Instrumentation Gas chromatograph Agilent 6890 Injection portSplit/splitless Column DB-5MS, 30 m × 0.32 mm × 1.0 mm Detector FIDSample introduction G1888 Data collection ChemStation

G1888 Headspace Conditions GC cycle time 30 minutes Oven temperature150° C. Loop temperature 180° C. Transfer line temperature 190° C. Vialequilibration time 30 minutes Shaking speed Off Loop fill time 0.20minutes Loop equilibration time 0.10 minutes Inject time 0.50 minutesPressurization time 0.50 minutes Advance functions Multi HS EXT on; 5extractions per vial

6890 GC Conditions Carrier gas (EPC) Nitrogen, 2.0 mL/min Inlettemperature 300° C. Split ratio 1:50 Flow mode Constant flow Aux 5 15psi FID temperature 300° C. Oven Program 50° C., hold for 3 min; ramp to280° C. at a rate of 15° C./min; hold for 2 minutes. (20.3 min in all)Detector FID @ 300° C.; Hydrogen 40 mL/min; Air 450 mL/min; Make up(Nitrogen) 45 mL/min

Multiple Headspace Extraction

MHE assumes that all of the analyte will be extracted thoroughly fromthe sample after unlimited headspace extraction steps. The theoreticalvalue of the total amount is calculated by the following formula:

${\ln \; A_{n}} = {{{- {K\left( {n - 1} \right)}} + {\ln \; A_{1}\mspace{14mu} {\sum\limits_{n = 1}^{\infty}A_{n}}}} = {A_{1}/\left( {1 - e^{- K}} \right)}}$

To calculate the total value by this formula, only two parameters areneeded, A₁ and K. A₁ is the peak area or analyte amount of the firstextraction. K is the slope of a linear relationship predicted betweenthe sequence number of extraction and the corresponding naturallogarithm of peak area or analyte amount. If the sample is a suitablesystem for application of multiple headspace extraction, a good fit willbe observed between extraction number and the logarithm of peak area.The methane concentration in plaque is calculated according calibrationcurve, correlation between peak area and methane concentration.

Calibration Curve

50, 100, 200, 300 and 500 uL pure methane gas is injected into a 20 mLheadspace vial separately, and then these samples are analyzed by GCwith the same GC condition. The calibration curve is provided in theFIG. 1

COMPARATIVE EXAMPLES (“CE”) AND ILLUSTRATIVE EXAMPLES (“IE”)

The effect of the coagent to peroxide ratio on the crosslinkablecompositions is determined by preparing CEs and IEs according to theformulations provided in Table 2, below, and using the materialsdescribed above and the sample preparation methods below. ThreeIllustrative Samples (IE1-IE3) and three Comparative Samples (CE1-CE3)are prepared according to the formulations provided in Table 2 below bysoaking DCP and TAIC, with or without acrylate TEMPO, into LDPE1 pelletsat 80° C. for 8 hours.

TABLE 2 Formulations of CE1-CE3 and IE1-IE3 Component CE1 IE1 CE2 IE2-1CE3 IE3 LDPE 1 98.5 98.34 98.6 98.44 98.45 98.29 Organic 0.75 0.75 0.950.95 0.6 0.6 Peroxide (DCP) Coagent 0.75 0.75 0.45 0.45 0.95 0.95 (TAIC)Radical 0.16 0.16 0.16 Scavenger (Acrylate TEMPO) Total 100 100 100 100100 100 Coagent/ 1.08 1.08 0.51 0.51 1.72 1.72 Peroxide Ratio (mol/mol)

Analyze CE1-CE3 and IE1-IE3 for curing behavior and methane productionusing the above-described Test Methods. The results are provided inTable 3 below.

TABLE 3 Properties of CE1-CE3 and IE1-IE3 Properties CE1 IE1 CE2 IE2-1CE3 IE3 ML, dN*m 0.22 0.20 0.22 0.19 0.22 0.18 MH, dN*m 3.71 3.55 3.823.63 3.26 3.32 MH-ML, 3.49 3.35 3.60 3.44 3.04 3.14 dN*m ts1 @ 180° 1.161.36 1.08 1.23 1.38 1.62 C., min. T90 @ 180° 4.27 4.52 4.16 4.30 4.805.163 C., min. Methane, ppm 301 273 385 336 205 209 ΔMethane, −28 −49 4ppm

The results from Table 3 show that the addition of acrylate TEMPO to acomposition comprising a crosslinking coagent, with a coagent toperoxide ratio of less than 1.72:1, provides for crosslinkablecompositions exhibiting decreased methane production, comparablecrosslink density, and improved scorch resistance. In particular, CE1and IE1 each contain identical formulations except that IE1 includesacrylate TEMPO and reduced ethylene-based polymer in a correspondingamount. IE1 exhibits comparable crosslink density, improved scorchtimes, and a nearly 10 percent decrease in methane production. Likewise,CE2 and IE2-1 contain identical formulations except that IE2-1 includesacrylate TEMPO and reduced ethylene-based polymer in a correspondingamount. IE2-1 exhibits comparable crosslink density, improved scorchtimes, and a nearly 13 percent decrease in methane production.

CE2, CE4-CE8 and IE2-2, IE4-IE8

The effect of various coagents on the crosslinkable compositions isdetermined by preparing CEs and IEs according to the formulationsprovided in Table 4, below, and using the materials described above andthe sample preparation methods below. Six Illustrative Samples (IE2-2,IE4-IE8) and six Comparative Samples (CE2, CE4 CE8) are preparedaccording to the formulations provided in Table 4 below by soaking DCPand coagents, with or without acrylate TEMPO, into LDPE1 pellets at 80°C. for 8 hours.

TABLE 4 Formulations of CE2, CE4-CE8 and IE2-2, IE4-IE8 Component CE2IE2-2 CE4 IE4 CE5 IE5 CE6 IE6 CE7 IE7 CE8 IE8 LDPE 1 98.60 97.88 98.4497.72 98.44 97.72 98.60 97.88 98.72 98.00 98.45 97.73 Organic Peroxide(DCP) 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95 0.95Coagent (TAIC) 0.45 0.45 Coagent (TMPTMA) 0.61 0.61 Coagent (TMPTA) 0.610.61 Coagent (TAC) 0.45 0.45 Coagent (HATATA) 0.33 0.33 Coagent (TATM)0.60 0.60 Radical Scavenger 0.72 0.72 0.72 0.72 0.72 0.72 (AcrylateTEMPO) Total 100 100 100 100 100 100 100 100 100 100 100 100Coagent/Peroxide 0.51 0.51 0.58 0.58 0.51 0.51 0.51 0.51 0.26 0.26 0.520.52 Ratio (mol/mol)

Analyze CE2, CE4 CE8 and IE2-2, IE4-IE8 for curing behavior and methaneproduction using the above-described Test Methods. The results areprovided in Table 5, below.

TABLE 5 Properties of CE2, CE4-CE8 and IE2-2, IE4-IE8 Properties CE2IE2-2 CE4 IE4 CE5 IE5 CE6 IE6 CE7 IE7 CE8 IE8 ML, dN*m 0.22 0.18 0.280.18 0.21 0.18 0.23 0.18 0.23 0.19 0.23 0.18 MH, dN*m 3.82 2.90 2.602.66 2.32 2.30 3.46 3.21 2.86 2.79 3.29 3.40 MH-ML, dN*m 3.60 2.72 2.322.48 2.11 2.12 3.23 3.03 2.63 2.60 3.06 3.22 ts1 @ 180° C., min. 1.082.27 1.54 1.87 2.00 2.49 1.12 2.10 1.34 2.07 1.19 1.89 T90 @ 180° C.,min. 4.16 5.91 4.69 5.39 5.12 5.67 4.23 5.77 4.31 5.26 4.41 5.37ts1@140° C., min. 41.91 109.68 54.37 97.01 63.00 99.71 42.32 96.02 50.5079.05 44.69 80.51 SI, min. 6.33 61.26 −3.10 43.51 −0.60 36.42 2.20 52.970.29 28.21 2.11 40.25 Methane, ppm 385 208 382 225 388 222 386 235 358218 370 231 ΔMethane, ppm −177 −157 −166 −151 −140 −139

The results from Table 5 show that the addition of acrylate TEMPO to acomposition comprising a crosslinking coagent, with a coagent toperoxide ratio of less than 1.72:1, provides for crosslinkablecompositions exhibiting decreased methane production, comparablecrosslink density, and improved scorch resistance. The IEs in Table 5each comprise acrylate TEMPO whereas the CEs do not. The IEs exhibitedcomparable crosslink density, improved scorch times, and decreases inmethane production.

CE2, CE9, IE2-2, IE9, and IE10

The effect of various TEMPO derivatives on the crosslinkablecompositions is determined by preparing CEs and IEs according to theformulations provided in Table 6, below, and using the materialsdescribed above and the sample preparation methods below. TwoIllustrative Samples (IE2-2 and IE9) and two Comparative Samples (CE2and CE9) are prepared according to the formulations provided in Table 6below by soaking DCP and TAIC, with or without TEMPO derivatives, intoLDPE1 pellets at 80° C. for 8 hours. IE10 is prepared by first blendingthe LDPE 1 and bis TEMPO in a Brabender mixer at 125° C. and a rotorspeed of 30 rpm. The resulting compound is extruded through asingle-screw extruder at 125° C. and pelletized. Then DCP and TAIC aresoaked into the pellets at 80° C. for 8 hours.

TABLE 6 Formulations of CE2, CE9, IE2-2, IE9, and IE10 Component CE2IE2-2 IE9 IE10 CE9 LDPE 1 98.60 97.88 97.92 97.88 98.10 Organic Peroxide0.95 0.95 0.95 0.95 0.95 (DCP) Coagent (TAIC) 0.45 0.45 0.45 0.45 0.45TEMPO 0.5 Radical Scavenger 0.72 (Acrylate TEMPO) Radical Scavenger 0.68(Allyl TEMPO) Radical Scavenger 0.72 (Bis TEMPO) Coagent/Peroxide 0.510.51 0.51 0.51 0.51 Ratio (mol/mol) Total 100 100 100 100 100

Analyze CE2, CE9, IE2-2, IE9, and IE10 for curing behavior and methaneproduction using the above-described Test Methods. The results areprovided in Table 7, below.

TABLE 7 Properties of CE2, CE9, IE2-2, IE9, and IE10 Properties CE2IE2-2 IE9 IE10 CE9 ML, dN*m 0.22 0.18 0.19 0.20 0.17 MH, dN*m 3.82 2.902.13 2.50 1.47 MH − ML, dN*m 3.60 2.72 1.94 2.30 1.30 ts1 @ 180° C.,min. 1.08 2.27 2.63 2.07 5.11 T90 @ 180° C., min. 4.16 5.91 5.47 5.027.42 ts1@140° C., min. 41.91 109.68 142.46 106.66 SI, min. 6.33 61.2672.93 48.65 Methane, ppm 385 208 279 210 199 ΔMethane, ppm −177 −106−175

The results from Table 7 show that various TEMPO derivatives (i.e.,acrylate TEMPO, allyl TEMPO, and bis TEMPO) are suitable for use withthe disclosed crosslinkable compositions. In particular, these TEMPOderivatives provide for crosslinkable compositions exhibiting decreasedmethane production, improved crosslink density, and improved scorchresistance.

CE2, CE10 and IE2-2, 2-3, 2-4 and IE11

Additional Examples are prepared according to the formulations providedin Table 8, below, and using the materials described above and thesample preparation methods below. Four Illustrative Samples (IE2-2, 2-3,24 and IE11) and two Comparative Samples (CE2 and CE10) are preparedaccording to the formulations provided in Table 8 below by soaking DCPand coagents, with or without TEMPO derivatives, into LDPE1 or LDPE 2pellets at 80° C. for 8 hours.

TABLE 8 Formulations of CE2, CE10 and IE2-2, 2-3, 2-4 and IE11 ComponentCE2 IE2-2 IE2-3 IE2 4 CE10 IE11 LDPE 1 98.6 97.88 98.12 98.22 LDPE 298.55 98.37 Organic 0.95 0.95 0.95 0.85 0.5 0.5 Peroxide (DCP) Coagent0.45 0.45 0.45 0.45 0.45 0.45 (TAIC) Coagent 0.5 0.5 (HATATA) Radical0.72 0.48 0.48 0.18 Scavenger (Acrylate TEMPO) Total 100 100 100 100 100100 Coagent/DCP 0.51 0.51 0.51 0.57 1.71 1.71 (mol/mol)

Analyze CE2, CE10 and IE2-2, 2-3, 2-4 and IE11 for curing behavior andmethane production using the above-described Test Methods. The resultsare provided in Table 9, below.

TABLE 9 Properties of CE2, CE10and IE12-2, 2-3, 2-4 and IE11 PropertiesCE2 IE2-2 IE2-3 IE2-4 CE10 IE11 ML, dN*m 0.22 0.18 0.18 0.19 0.19 0.17MH, dN*m 3.82 2.90 3.54 3.02 3.21 2.90 MH-ML, 3.60 2.72 3.36 3.36 3.022.73 dN*m ts1 @ 180° 1.08 2.27 1.63 1.92 1.39 1.92 C., min. T90 @ 180°4.16 5.91 5.06 5.34 4.67 5.43 C., min. Methane, ppm 385 208 281 216 194160 Δmethane, ppm −177 −104 −169 34

The results from Table 9 show that the IEs provide for crosslinkablecompositions exhibiting decreased methane production, improved crosslinkdensity, and improved scorch resistance.

1. A crosslinkable polymeric composition, comprising: an ethylene-basedpolymer; an organic peroxide; a crosslinking coagent; and amethyl-radical scavenger comprising at least one derivative of2,2,6,6-tetramethyl-1-piperidinyloxy, wherein the ratio of crosslinkingcoagent to organic peroxide is less than 1.72:1 on a molar basis.
 2. Thecrosslinkable polymeric composition of claim 1, wherein theethylene-based polymer is selected from the group consisting oflow-density polyethylene, linear-low-density polyethylene,very-low-density polyethylene, and combinations of two or more thereof.3. The crosslinkable polymeric composition according to claim 1, whereinthe organic peroxide is selected from the group consisting of dicumylperoxide, tert-butyl peroxybenzoate, di-tert-amyl peroxide,bis(alpha-t-butyl-peroxyisopropyl) benzene, isopropylcumyl t-butylperoxide, t-butylcumylperoxide, di-t-butyl peroxide,2,5-bis(t-butylperoxy)-2,5-dimethylhexane,2,5-bis(t-butylperoxy)-2,5-dimethylhexyne-3,1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, isopropylcumylcumylperoxide, butyl 4,4-di(tert-butylperoxy) valerate,di(isopropylcumyl) peroxide, and combinations of two or more thereof. 4.The crosslinkable polymeric composition according to claim 1, whereinthe crosslinking coagent is selected from the group consisting oftriallyl isocyanurate, triallyl cyanurate, triallyl trimellitate,trimethylolpropane triacrylate,N2,N2,N4,N4,N6,N6-hexaallyl-1,3,5-triazine-2,4,6-triamine andcombinations of two or more thereof.
 5. The crosslinkable polymericcomposition according to claim 1, wherein the crosslinking coagentcomprises a blend of crosslinking coagents.
 6. The crosslinkablepolymeric composition according to claim 1, wherein the at least onederivative of 2,2,6,6-tetramethyl-1-piperidinyloxy is selected from thegroup consisting of 4-acryloxy-2,2,6,6-tetramethylpiperidine-N-oxyl,4-allyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl, andbis(2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl) sebacate, andcombinations of two or more thereof.
 7. The crosslinkable polymericcomposition of claim 1, further comprising one or more additivesincluding, but not limited to, scorch retardants, antioxidants,processing aids, fillers, coupling agents, ultraviolet absorbers orstabilizers, antistatic agents, nucleating agents, slip agents,plasticizers, lubricants, viscosity control agents, tackifiers,anti-blocking agents, surfactants, extender oils, acid scavengers, flameretardants, and metal deactivators.
 8. The crosslinkable polymericcomposition of claim 1, wherein the ethylene-based polymer is present inan amount ranging from 90 to 99.9 weight percent, based on the entirecrosslinkable polymeric composition weight, wherein the organic peroxideis present in an amount of less than 3 weight percent, based on theentire crosslinkable polymeric composition weight, wherein thecrosslinking coagent is present in an amount ranging from 0.2 to 1weight percent, based on the entire crosslinkable polymeric compositionweight, wherein the methyl-radical scavenger is present in an amountranging from 0.05 to 1 weight percent, based on the entire crosslinkablepolymeric composition weight.
 9. A crosslinked polymeric articleprepared from the crosslinkable polymeric composition according toclaim
 1. 10. A cable core, comprising: a conductor; a first polymericsemiconductive layer at least partially surrounding the conductor; aninsulation layer at least partially surrounding the first polymericsemiconductive layer and comprising the crosslinked polymeric article ofclaim 9; and a second semiconductive layer at least partiallysurrounding the insulation layer.